摘要
针对2023年12月18日甘肃积石山M_(S)6.2地震,基于AM_(S)R2微波亮温数据,使用基于小波分析的两步差法提取了地震前的微波亮温异常,对震前异常的时间、空间和强度演化特征进行了总结分析,并探讨了微波异常的产生机理。结果显示:空间上,震前微波异常呈高温条带与低温区域相间的“//”形分布格局;时间上,两高温条带的微波异常在达到峰值后大幅度降低,存在震前平静期。此外,积石山地震微波异常的空间分布格局与岩石加载热红外观测实验结果具有一定的相似性,可能表征了地震前地壳岩体内微破裂的大规模发育。进一步结合遥感-岩石力学实验和亚失稳模型推断地震前微波异常主要是地应力变化所致,并且震前的异常平静期是地壳应力进入亚失稳阶段的标志,对地震的发生具有重要的前兆指示意义。
On December 18,2023,a M_(S)6.2 earthquake occurred in Jishishan county,Gansu Province,causing significant casualties and serious economic losses.This earthquake occurred in the northeastern margin of the Qinghai-Xizang Plateau,which is at the junction of the Loess Plateau and the Qinghai-Xizang Plateau.A series of studies have been conducted on this earth-quake,primarily focusing on damage assessment or focal mechanism solution.However,from a broader perspective of earthquake precursor research,it has been documented that thermal ra-diation anomalies have been detected prior to many moderate or strong earthquakes.And,the detection of pre-earthquake anomalies for the 2023 Jishishan earthquake is still scarce.Whether there were thermal radiation anomalies prior to Jishishan earthquake is a scientific question worthy of exploring.Currently,there are mainly two types of satellite remote sensing data sources utilized to detect pre-earthquake thermal radiation anomalies,one is the thermal infrared remote sensing data,the other is the passive microwave remote sensing data.However,due to the limited atmosphere penetration capability of thermal infrared band,data-continuity of satellite thermal infrared remote sensing is strongly affected by the variant meteorological conditions.In con-trast,passive microwave remote sensing data offer unique advantages in terms of data continu-ity for the detection of pre-earthquake thermal radiation anomalies,thanks to its longer wave-lengths and stronger atmospheric penetration capability.To answer the abovementioned scientific question,the microwave brightness temperature(MBT)data covering(34°N−42°N,99°E−110°E)acquired by the Advanced Microwave Scanning Radiometer 2(AM_(S)R2)sensor is collected.This dataset is analyzed using a novel wavelet-based two-step difference(WTSD)method to detect the thermal radiation anomalies preceding the Jishishan earthquake.In the WTSD method,the radiation received by microwave sensors is considered to com-prise three different components,i.e.,the low-frequency background field,high-frequency meteorological signals,and the seismic MBT anomalies.The low-frequency background field is considered as a stable contribution to the microwave radiation,which is mainly caused by topography,surface coverage and seasonal variations with strong regularity.The high-frequency meteorological signals are mainly caused by frequent variation of the meteorological conditions(e.g.,precipitation and temperature change,etc),which are considered as a ran-dom contribution.The seismic MBT anomalies can be extracted by sequentially subtracting the low-frequency background field and the high-frequency meteorological signals from the origin-al MBT data.Specifically,the hierarchical clustering is first conducted to classify the ground covers into different types.Then,MBT background fields for different types of ground covers are established and removed separately by adopting wavelet decomposition on the multi-year MBT data(from 2003 to 2022).After that,a second wavelet decomposition is performed to eliminate the high-frequency meteorological signals,thereby extracting the MBT anomalies as-sociated with the Jishishan earthquake.The temporal,spatial,and intensity evolution charac-teristics of the pre-earthquake MBT anomalies for the Jishishan earthquake are summarized as follows:1)Temporally,the MBT anomalies lasted for approximately 133 days(from August 7 to December 18,2023)and experienced three different periods,i.e.,the initial active period,the subsequent calm period and the final pre-earthquake rebound period.2)Spatially,a“//”-shaped distribution was found preceding the earthquake,consisting of MBT increase stripes interspersed with a MBT decrease region.During the active period,two MBT increase stripes appeared,and then gradually extended in the northeastern margin of the Qinghai-Xizang Plateau,forming a“//”-shaped anomalies distribution pattern.However,there was a MBT decrease region between the two MBT increase stripes.3)In terms of intensity,the maximum intensity within both MBT increase stripes ex-ceeded 10 K,and the daily average intensity within them reached 3 K.It was worth noting that on 19 November(one month preceding the earthquake),both MBT increase stripes showed sig-nificant MBT anomalies decrease of approximately 7 K.Meanwhile,the MBT in the decrease region had been consistently at a low level,with a maximum intensity of less than 2 K.On October 10(approximately two months prior to the earthquake),the MBT anomalies in the de-creasing region also exhibited a significant decrease of around 12 K.Generally,the evolution trend of the MBT decrease region was similar to that of the two MBT increase areas,but in the MBT decrease region,the amplitude of the anomalies was smaller,the calm period was earlier and its decrease amplitude was larger.Interestingly,the spatial distribution of the MBT anomalies preceding Jishishan earth-quake is similar to the infrared anomalies observed during our rock-loading experiment.This indicates a large-scale development of microfractures within the crust preceding the earthquake.According to the remote sensing rock mechanics experiments and the meta-instability model,it can be concluded that the pre-earthquake MBT anomalies are mainly caused by variation of the crustal stress.The calm period shortly preceding the earthquake may imply that the crustal stress has entered the meta-instability stage,which can be regarded as a precursor to the Jishishan earthquake.
作者
崔华朔
刘善军
魏恋欢
王蜜
刘文芳
韩鑫
Cui Huashuo;Liu Shanjun;Wei Lianhuan;Wang Mi;Liu Wenfang;Han Xin(School of Resources and Civil Engineering,Northeastern University,Shenyang 110819,China)
出处
《地震学报》
2025年第5期677-694,共18页
Acta Seismologica Sinica
基金
国家自然科学基金(41930108)资助.
关键词
2023
年积石山
M_(S)6.2
地震
微波亮温异常
时空演化
地壳应力
遥感-岩石力学实验
M_(S)6.2 Jishishan earthquake in 2023
microwave brightness temperature anom-alies
spatio-temporal evolution
crustal stress
remote sensing-rock mechanics experiment
作者简介
崔华朔,在读硕士研究生,主要从事地震微波遥感方面的研究,e-mail:15275740100@163.com;通信作者:魏恋欢,博士,副教授,主要从事灾害遥感与微波遥感研究,e-mail:weilianhuan@mail.neu.edu.cn。
